The present invention relates to a manual transmission unit for use in a vehicle, and more particularly to an improvement in the manual transmission unit possessing synchronizers and at least one unsynchronized gear, such as a reverse one.
A widely known manual transmission has input and output shafts supported in a parallel relationship to each other within a housing assembly for the unit, an idler shaft supported in a parallel relationship to the shafts from the housing assembly, driving and driven gears respectively mounted on the input and output shafts, an idler gear which is axially slidable on the idler shaft, a folk shaft which is slidably supported in a parallel relationship to the idler shaft from the housing assembly and is operatively connected to a manual shift lever which is selectively shifted from its neutral position to a forward or reverse position, a detent mechanism mounted on the housing assembly for selectively retaining the fork shaft in its neutral and shifted positions under a resilient load acting thereon, a shift head member which is slidable on the fork shaft, a one-way engagement mechanism for effecting the engagement of the shift head member with the fork shaft through the axial movement of the fork shaft toward and away from its reverse position, and a shift arm member pivoted to the inner wall structure of the housing assembly and linked with the shift head member, wherein the idler gear is carried by the shift arm member to be retained in its neutral position and to be engaged with the driving and driven gears through the axial movement of the fork shaft to its reverse position.
The reverse gear is usually constructed so that it is unsynchronized. Therefore, even after the vehicle comes to a complete stop, the input shaft, which runs into the transmission, is still rotating because of inertia. Hence, if an operator shifts into reverse while the input shaft is still rotating, a grinding noise may generate in the transmission resulting from the engagement between a rotating reverse driving gear, which is connected to the input shaft, and a stationary reverse idler gear. This results in discomfort to the operator and undesired wear on the gears.
To overcome the foregoing drawbacks, U.S. Application Ser. No. 532,480 (Filing Date, Sept. 15, 1983) TOTALLY SYNCHRONIZED MANUAL TRANSMISSION UNITS FOR USE IN A VEHICLE has been proposed. According to this proposed invention, a holder member is employed for holding shift heads except selected shift head when a select operation is made by an operator. When a reverse speed is selected, synchronizers for forward positions is effected to decrease or stop the rotation of the input shaft caused by inertia, thereby resulting in the decrease in a grinding noise generated by the engagement between a rotating reverse driving gear and a stationary reverse driven gear.
However, according to this proposed apparatus, a sleeve, on which a reverse driven gear is provided, is axially displaced at a reverse shift, resulting in the synchronization by the synchronizer employed at a reverse shift. It is not preferable to effect such a synchronizer, from the standpoint of the endurance of the synchronizer.